1. Field of the Invention
This invention relates to semiconductor lasers and in particular to techniques for controlling the light output of such devices.
2. Description of the Prior Art
Semiconductor lasers may be made highly intrinsically efficient at low frequencies, but the minimum input power required to control them is still high enough to require drivers between the semiconductor lasers and low power input sources, such as logic circuitry. At higher frequencies, the problem is compounded by the lower intrinsic efficiency available with conventional designs. High frequency, or high bit rate, systems using conventional semiconductor lasers require preamplifying stages between the source of the control signal and the lasing device.
Similarly, control of semiconductor lasers by optical input signals conventionally requires several stages of conversion, from optical to electrical to more powerful optical signals.
The additional circuitry, power and physical requirements resulting from these difficulties limits the level of complex signal handling conveniently achievable with conventional semiconductor laser devices. What are needed are techniques and devices for generating and controlling emitted light from semiconductor lasers which obviate the need for additional levels of amplification, preamplification and/or conversion of electrical and/or optical input signals. In particular what are needed are semiconductor laser devices capable of more than 100% differential quantum efficiency, that is, of directly controlling an optical output signal with an optical or electrical input signal of lower energy.